Recommended Items

Rings

Armor

By Depth 5, your armor should at least be absorbing up to 12 Damage (or as close as you can get to 12), or higher, so you can survive Goo, since it can deal a max damage of 12 per (melee) attack.
[NOTE:
Unless received via Hero's Remains, you'll be hard-pressed to obtain armor with up to 30 Damage Absorption (or even be strong enough to equip said armor), in order to mitigate Goo's alternate, ranged attack ("Pumped Up"), which can deal a max damage of 30 per attack.
So, it's crucial/imperative to at least have an Earthroot seed for this Boss Fight (for Melee-centric combat); and if you have a Ring of Evasion and/or an Entanglement-inscribed armor, then all the better.
It should go without saying, but those taking the Ranged-centric combat approach won't have to worry about Goo's "Pumped Up" attack, especially if you can disable Goo before it can even launch said attack.]

+4Leather Armor (Only if found from dungeon, or received from Sad Ghost; never waste Upgrade scrolls on Leather Armor; Wear as interim armor only)

+2Mail Armor (Only if found from dungeon, or received from Sad Ghost; avoid wasting Upgrade scrolls on Mail Armor; Wear as interim armor only)

+1Scale Armor (Only if found from dungeon, or received from Sad Ghost; avoid wasting Upgrade scrolls on Scale Armor; Wear as interim armor only)

Recommended Debuffs

Combat Methods

Since you have no Ankh to give you another chance, you'll solely be relying on a (hopefully) Full Dew Vial. It's all, or nothing, so if you feel that you have adequate equipment to take Goo on, go for it.If you feel that you don't, after having made it this far, you can attempt to face Goo anyway, or deliberately let yourself die, so that one of your equipped items can be passed on to the next attempt, via Hero's Remains.

Note:
After clearing Depth 4, but before descending to Depth 5, is usually one of the best times to identify any scrolls you have.The other time would be after defeating Goo, but before descending to Depth 6.

WARNING:
Once you step off the stairs at Depth 5, THE STAIRS WILL DISAPPEAR & you'll be UNABLE TO LEAVE until Goo is defeated.
Be sure you're absolutely ready to face Goo, before descending to D-5!
__________________________________________________________

Melee Method

The Glyph of Entanglement/Bounce/Viscosity is recommended for this boss fight.

[If wishing to utilize the door's Surprise Attack mechanism, Bounce would be the best option here, as it would give all your strikes 100% accuracy, while pushing Goo away, periodically making it miss its Pumped Up attack. Alternatively, Viscosity will convert Goo's Pumped Up burst/front-loaded damage into a more manageable damage-over-time.]

Utility Items Needed:

Seed of Earthroot

Scroll of Lullaby

Wand of Slowness

Wand of Amok

Wand of Flock

Ring of Evasion

Ring of Haste

Ring of Accuracy

This is the most common & straightforward approach between the two, and can be accomplished using only Damage-Over-Time debuffs (+ Herbal Armor)/without Crowd Control debuffs, especially if used in conjunction with the Surprise Attack tactic.

Along with your melee weapon of choice, you'll also need most of the listed Utility items to successfully defeat Goo.
You don't need all of them to succeed, but having each item will certainly increase your chances of success with this method.

Once you're ready, descend to Depth 5.

On your way to Goo's room, check for hidden traps & take note of the amount of water tiles you pass along the way, particularly if there are any right beside the doors (either/both sides). The amount of water tiles at D-5 is a significant determining factor in your success/defeat against Goo (being able to wash off Caustic Ooze/Goo being able to heal on water).
→ If using the Surprise Attack door tactic, be sure there's a water tile by the door (usually, right outside Goo's room, but can be done with either door & on either side, but only after kiting Goo), and plant/throw a Seed of Earthroot on it, to set things up for the fight.
→ If not, then planting/throwing a Seed of Earthroot on any water tile should suffice (though you might want to opt for one in Goo's room, as the room has the most space, especially if you also plan on using any of the Crowd Control methods below).
Once you step into the doorway (to wake up Goo), if Goo hasn't woken up from your entry, this would be the perfect time to unleash your DoT arsenal, particularly your Golden Bees & Mirror Images. Though you may want to throw a Curaré Dart/ Bomb/fire a Wand of Avalanche first, to lock Goo down, before throwing a Tomahawk (or waking Goo up with a Tomahawk, if you don't have any Paralyzed-inflicting items) & following up with your summons, T-Gas potion, & DoT seeds (Firebloom & Sorrowmoss) in Goo's path to you.
If it's woken up upon your entry, then just go straight to throwing the DoT seeds in its path, the T-Gas potion, & then the summons (in that order).
If using the Surprise Attack door tactic, save the Sorrowmoss seed last for after you've awoken & kited Goo to the door. Once you step into the doorway, plant the Sorrowmoss seed, then step onto the Earthroot seed you planted earlier. This way, not only will Goo get surprise-attacked, but it'll also incur DoT damage from the Sorrowmoss plant during the fight, expediting the fight. If you have a Bounce-inscribed armor, you'll be able to replant more seeds in the door whenever Goo gets pushed back into its room.
If you're not using the door, then you don't need to save the Sorrowmoss seed for planting it at the door.

Once the fight has started, feel free to choose any of the following approaches that are available to you (if most/all are available, weave them all together), keep striking, & repeat the rotation, until Goo's defeated:

This crowd control method's straightforward, as slowing Goo down will decrease its damage output & lessen the amount of times it uses its Pumped-up ranged-attack (which, you REALLY want, cause that mess HURTS).

[If you don't have a Chilling-enchanted weapon, go ahead & use the Wand of Slowness, if you have one.]

Then unleash your DoT arsenal & keep striking Goo.

Repeat the rotation until Goo's defeated.

This Crowd Control tactic can also be combined with other tactics (namely Amok & Terror), in order to gain more turns & distance from Goo.

Don't forget to pick up Lloyd's Beacon, if Goo dropped it, and make sure you find & raid/loot the Rat King's room (inside Goo's room) before descending to D-6/Stage 2/Prison stage.
This would also be the perfect time to identify any unidentified scrolls, if you haven't already done so at D-4.
If you're trying to save gold, feel free to purchase the unidentified scrolls at the D-6 Shop before identifying them here at D-5.
The downside to that, though, is that you may end up wasting more gold by wasting a scroll like Magic Mapping at D-5.
So the choice is yours, on whether you want to save money by buying unidentified scrolls (i.e. extra Magic Mapping), but risking a "Russian Roulette" (e.g. Challenge scroll) by identifying them at D-6, or taking a small hit in gold (& 1 Magic Mapping scroll), but playing it safe, so that you don't risk reading a Challenge at D-6. (More money VS Increased survival chances)

This crowd control method's simple & easy, since you'll be able to avoid Goo's damage (Caustic Ooze & Pumped up) altogether.
However, it'll take longer to be able to take advantage of the Surprise Attack door tactic, since you need to lure Goo out of its room first, as there's space for the sheep in Goo's room, but not in the hallway.
But if you're not using the surprise attack door tactic (& there's hopefully a water tile in Goo's room), go ahead & plant an Earthroot seed on a water tile, step on it, & initiate the fight.

Be sure to fire the Wand of Flock beside (not between) your Hero/ine & Goo, when Goo is still 1 tile away, so that your next turn is to fire the Wand of Amok at Goo before it executes its very first attack. Once Goo is Amok'ed, strike away at Goo until right before the sheep fade & the Amok debuff ends, to be able to smoothly repeat the rotation without getting hurt.

Note: You won't be able to take advantage of Surprise Attacks with this method, unless you have a Stunning enchanted weapon (or manage to melee-equip & successfully land a Curaré Dart on Goo, with a Rogue/Huntress).

Repeat the rotation until Goo's defeated.

This Crowd Control tactic can also be combined with another tactic (namely Crippled/Slowed), in order to gain more turns to defeat Goo.

Don't forget to pick up Lloyd's Beacon, if Goo dropped it, and make sure you find & raid/loot the Rat King's room before descending to D-6/Stage 2/Prison stage.
This would also be the perfect time to identify any unidentified scrolls, if you haven't already done so at D-4.
If you're trying to save gold, feel free to purchase the unidentified scrolls at the D-6 Shop before identifying them here at D-5.
The downside to that, though, is that you may end up wasting more gold by wasting a scroll like Magic Mapping at D-5.
So the choice is yours, on whether you want to save money by buying unidentified scrolls, but risking a "Russian Roulette" (e.g. Challenge scroll) by identifying them at D-6, or taking a small hit in gold, but playing it safe, so that you don't waste any needed scrolls (e.g. Magic Mapping scroll).

This crowd control method's also as straightforward as the above methods, provided you have the items to inflict Paralyzed (or the Class, to be able to inflict said debuff).

With Stunning/equipped Curaré Darts, you won't even need the door, since Paralyzed enables Surprise Attacks/100% Accuracy with each strike. Just make sure you're still standing on water, in case Goo's able to sneak in a Caustic Ooze-laced attack whenever the Paralyzed debuff is down.

Inflict Paralyzed, follow up with your DoT arsenal, then strike away 'til the debuffs end & need to be reapplied.

Repeat the rotation until Goo's defeated.

Don't forget to pick up Lloyd's Beacon, if Goo dropped it, and make sure you find & raid/loot the Rat King's room before descending to D-6/Stage 2/Prison stage. This would also be the perfect time to identify any unidentified scrolls, if you haven't already done so at D-4.
If you're trying to save gold, feel free to purchase the unidentified scrolls at the D-6 Shop before identifying them here at D-5.
The downside to that, though, is that you may end up wasting more gold by wasting a scroll like Magic Mapping at D-5.
So the choice is yours, on whether you want to save money by buying unidentified scrolls, but risking a "Russian Roulette" (e.g. Challenge scroll) by identifying them at D-6, or taking a small hit in gold, but playing it safe, so that you don't waste any needed scrolls (e.g. Magic Mapping scroll).

D-5 Hallway:
[Note: This can only be done with a (mostly) dry hallway. Also, the hallway should already be cleared of traps before initiating the fight.]

Once the hallway is cleared of traps & you've planted your own, position yourself at the end of the hallway, opposite from Goo's room.(Depending on your performance, you may, or may not, want to stand on an Earthroot in water.)

Read the Challenge scroll to beckon Goo to you (may require tapping the Wait button a few times).
As soon as Goo enters the hallway, throw a Tomahawk at it to inflict Bleeding, then immediately throw a T-Gas potion midway between you & Goo.Not only will Goo be forced to trigger your traps, but it'll be forced to walk through the toxic gas as well.
By the time Goo reaches you, it'll be significantly damaged, expediting the fight.
If using Terror scrolls, allow it to reach you, so you can strike it with your main melee weapon for some damage, before inflicting Terror.
If using an Eldritch-enchanted weapon, summon an Allied NPC to deal extra damage (Golden Bee/Mirror Image), before it reaches melee distance of you & your weapon procs Terror.
And as it walks away, reset your DoT plant traps for Goo to walk on again, as the Terror debuff ends & it returns to you.

This method will be most effective (in recalling Goo) with a decent supply of Challenge & Terror scrolls, or an Eldritch-enchanted weapon, as you'll have Goo walking back & forth in the toxic gas, with DoT debuffs, essentially making Goo end itself.

Door Tactic:
If fighting by the door, you'll be able to take advantage of the 100% Surprise Attack mechanism throughout the fight. Though, this method may take a while, unless you have a Challenge scroll.

→ If Goo's asleep upon entry & is nearby, initiate by inflicting Bleeding with a Tomahawk; if Goo's asleep & at the opposite end of the room, initiate the fight with throwing a T-Gas potion at the opposite end of the room.
→ If Goo's awoken upon entry, immediately throw a T-Gas potion at the opposite end of the room. Wait until the 10th turn of Terror, or until Goo opens the door, to inflict Bleeding.

Then immediately follow-up with inflicting Poisoned; then Burning (but only if Goo's at the furthest cell from the door, so it doesn't burn the door down).
If Goo is near the door, immediately follow Poisoned with Honeypot/ Golden Bee, then Mirror Images, instead of Burning.
Once you've unleashed your DoT arsenal, back out of the doorway & wait for Goo to approach you & open the door.
You may want to stand on an Earthroot plant on top of water, in order to mitigate Goo's damage, until you proc Terror, or read a Terror scroll.
Strike Goo for some damage, then read a Terror scroll, or strike Goo until Eldritch procs Terror on Goo.

Repeat the rotation until Goo's defeated.

Don't forget to pick up Lloyd's Beacon, if Goo dropped it, and make sure you find & raid/loot the Rat King's room before descending to D-6/Stage 2/Prison stage. This would also be the perfect time to identify any non-identified scrolls, if you haven't already done so at D-4.
If you're trying to save gold, feel free to purchase the non-identified scrolls at the D-6 Shop before identifying them here at D-5.
The downside to that, though, is that you may end up wasting more gold by wasting a scroll like Magic Mapping at D-5.
So the choice is yours, on whether you want to save money by buying non-identified scrolls, but risking a "Russian Roulette" (e.g. Challenge scroll) by identifying them at D-6, or taking a small hit in gold, but playing it safe, so that you don't waste any needed scrolls (e.g. Magic Mapping scroll).

This Crowd Control tactic can also be combined with other tactics (namely Crippled/Slowed), in order to gain more turns to damage Goo.

This is likely the rarest, least-considered, most uncommon method one can come up with, but it's still very doable.
Although, this may require a player who's highly experienced with the Stench glyph's mechanisms, or a highly-skilled PD veteran (& overall gamer), as your Hero/ine will need to walk on water tiles during the entire fight.

→ If Goo's asleep upon entry, initiate the fight by inflicting Bleeding with the Tomahawk, then summon your Allied NPC's (Golden Bee{s}, then Mirror Images).
→ If Goo's awoken upon entry, initiate the fight by summoning your Allied NPC's (Golden Bee{s}, then Mirror Images). Inflict Bleeding later, if/when you decide to walk through the door & Goo follows you (so Surprise Attack allows you to land the Tomahawk).

Then immediately follow-up with inflicting Poisoned, then Burning.
Immediately head for (a) water tile(s) (while making sure Goo stays off of water), then let Goo catch up to you, so it can proc Stench.
Strike Goo twice, then diagonally move away from Goo, so that the toxic gas damages Goo, but you remain unharmed (since gas spreads cardinally).
Be mindful to move away whenever Goo's Pumped Up, so it doesn't burst you; avoiding Pumped Up's high damage takes priority, over dealing damage & kiting Goo into Stench's toxic gas.

Basically, this method will be similar to fighting the Fetid Rat.

Repeat the rotation until Goo's defeated.

Don't forget to pick up Lloyd's Beacon, if Goo dropped it, and make sure you find & raid/loot the Rat King's room before descending to D-6/Stage 2/Prison stage. This would also be the perfect time to identify any unidentified scrolls, if you haven't already done so at D-4.
If you're trying to save gold, feel free to purchase the unidentified scrolls at the D-6 Shop before identifying them here at D-5.
The downside to that, though, is that you may end up wasting more gold by wasting a scroll like Magic Mapping at D-5.
So the choice is yours, on whether you want to save money by buying unidentified scrolls, but risking a "Russian Roulette" (e.g. Challenge scroll) by identifying them at D-6, or taking a small hit in gold, but playing it safe, so that you don't waste any needed scrolls (e.g. Magic Mapping scroll).

Ranged Method

The Glyph of Affection is recommended for this boss fight.

[Under normal circumstances, Displacement is recommended over Affection, especially for non-Boss Depths, but since teleportation, and therefore Displacement, doesn't work at Boss Depths, this is the only other alternative for players taking the Ranged route {if your armor isn't already inscribed with Displacement in the first place}.
Basically, if you get Displacement, stick with it. If you don't & you get Affection, settle with it.
However, if you do get Displacement, you'll need a Wand of Blink to do what Displacement usually does at non-boss depths.]

Utility Items Needed:

Seed of Dreamweed

Potions of Invisibility (~5 max)

Scrolls of Terror (8 max)

Scrolls of Recharging

Scrolls of Lullaby

Curaré Darts

Javelins

Bombs

Wand of Avalanche

Wand of Blink

Wand of Slowness

Wand of Regrowth

Wand of Amok

Wand of Flock

Ring of Power

Ring of Accuracy

Ring of Haste

Frozen Carpaccio's

[For an illustration, please refer to the Goo section of TheDarkoko's Sniper Guide.]

For most players, this approach seems to be the rarer, more toweringly difficult of the two, unless you're a highly experienced, veteran Ranged Combat player/specialist.
However, it's actually deceptively simple & only slightly more difficult than the melee approach, if only because of the extra steps one needs to take. And with the right tools, it's very possible to accomplish.

Along with your ranged damage sources, you'll also need most of the listed Utility items to successfully defeat Goo.
You don't need all of them to succeed, but having each item will certainly increase your chances of success with this method.

Once you're ready, descend to Depth 5.

On your way to Goo's room, check for hidden traps & take note of the amount of water tiles you pass along the way (as well as any in Goo's room).
The amount of water tiles at D-5 is a significant determining factor in your success/defeat against Goo (being able to wash off Caustic Ooze/Goo being able to heal on water).
Then, you must determine whether you plan to fight Goo in its room, or in the hallway.
Generally, you'll want to fight Goo where it's most dry, save for 1 water tile, for you to stand on & wash off its Caustic Ooze.
But for the ranged approach, if you have nothing to immobilize Goo with (or otherwise maintain distance), you'll be moving around a lot; and you'll want to keep Goo away from water, so it doesn't heal. So, the difficulty of your fight will largely depend on the arsenal you've been able to gather, which will determine your strategy/tactics.

Once you're ready to awaken Goo, choose any of the following approaches that match the items you have (if you have items for multiple strategies, feel free to weave them all together, to expedite the fight):

[Note: You'll definitely need a Wand of Blink + a bunch of Recharging scrolls and/or an upgraded Ring of Power for this method.]

You've got your work cut out for you with this method, as you'll need to move around constantly & maintain distance from Goo, in order to inflict your DoT arsenal & attack it unscathed; and you'll need to do so while keeping Goo away from water. It won't be as difficult if D-5 doesn't generate many water tiles in Goo's room, but the trade-off is that, if Goo manages to inflict its Caustic Ooze debuff on you, then you'll keep receiving DoT damage 'til you wash it off.

Once you enter Goo's room to wake it up, (if it's still asleep & you have a Tomahawk) lead with Bleeding, then Crippled/ Slowed, then Poisoned, then Burning, then your Allied-Summons.
Then, find a strip/patch of water you can remain on top of while blinking back & forth. Position yourself, so that Goo will always move on dry floor, while it follows to attack you.

Keep attacking & blinking away, 'til right before the debuffs end & need to be reapplied. Additionally, between rotations is the perfect time to summon your allied NPC's.
(After the 1st rotation, Crippled/ Slowed need to be inflicted first, before inflicting your DoT arsenal.)

Repeat the rotation until Goo's defeated.

Don't forget to pick up Lloyd's Beacon, if Goo dropped it, and make sure you find & raid/loot the Rat King's room before descending to D-6/Stage 2/Prison stage. This would also be the perfect time to identify any unidentified scrolls, if you haven't already done so at D-4.
If you're trying to save gold, feel free to purchase the unidentified scrolls at the D-6 Shop before identifying them here at D-5.
The downside to that, though, is that you may end up wasting more gold by wasting a scroll like Magic Mapping at D-5.
So the choice is yours, on whether you want to save money by buying unidentified scrolls, but risking a "Russian Roulette" (e.g. Challenge scroll) by identifying them at D-6, or taking a small hit in gold, but playing it safe, so that you don't waste any needed scrolls (e.g. Magic Mapping scroll).

This Crowd Control tactic can also be combined with other tactics (namely Rooted, Charmed, Sleep, & Vertigo), in order to get more turns & distance from Goo.

The difficulty of this method will also largely depend on the amount of water tiles in Goo's room, since too much water will only provide Rooted, but prevent vegetation from growing, which prevents you from taking advantage of the vegetation to burn Goo with; however, it's still generally easier than only having Crippled/Slowed.

The process here is also largely similar to the Crippled/ Slowed method above, but with Rooted instead.
The extra nuance here is being able to fill Goo's room with vegetation, then proceed to light the whole room on fire, damaging Goo with Burning on a much larger scale, which will expedite the fight.
It'll also be easier to maintain distance for more turns to attack, since it's a Root, rather than a Slow; which is magnified when in possession of a Wand of Blink.
Additionally, this method can also be done in the hallway, provided that it's mostly dry.

(Remember to keep Goo away from water, and to wash off Goo's Caustic Ooze whenever it manages to inflict the debuff on you.)

Hallway:
→ If the hallway is long enough, dry, & any hidden traps have been disarmed, fill it up with vegetation first (then trample it), before getting Goo's attention & leading it there.
Once you've led it to the hallway, Root it, then unleash your DoT arsenal, saving Burning for last. This way, it'll receive plenty of damage before the whole hallway is ignited & Goo burns in the fire trying to make it's way towards you.
As it approaches, keep attacking it & inflicting any DoT debuff that ends before it reaches you.
Re-zap Regrowth & ignite the vegetation as needed, in order to keep Goo burning in the hallway for as long as you can, before it reaches you.
If Goo reaches you with plenty of remaining health, just keep inflicting the DoT debuffs while you kite it back to the depth's entrance door, so you can make a U-turn & repeat the process from the opposite direction/side of the hallway. (Just make sure Burning ends before Goo reaches the door, so you can capitalize on the door's Surprise Attack mechanism.)

Repeat the rotation until Goo's defeated.

Don't forget to pick up Lloyd's Beacon, if Goo dropped it, and make sure you find & raid/loot the Rat King's room before descending to D-6/Stage 2/Prison stage. This would also be the perfect time to identify any unidentified scrolls, if you haven't already done so at D-4.
If you're trying to save gold, feel free to purchase the unidentified scrolls at the D-6 Shop before identifying them here at D-5.
The downside to that, though, is that you may end up wasting more gold by wasting a scroll like Magic Mapping at D-5.
So the choice is yours, on whether you want to save money by buying unidentified scrolls, but risking a "Russian Roulette" (e.g. Challenge scroll) by identifying them at D-6, or taking a small hit in gold, but playing it safe, so that you don't waste any needed scrolls (e.g. Magic Mapping scroll).

This Crowd Control tactic can also be combined with other tactics (namely Crippled/Slowed, Charmed, & Sleep), in order to get more turns & distance from Goo.

This method is very straightforward; and it requires either plenty of Recharging scrolls, an upgraded Ring of Power, or both, to sustain multiple rotations during the entire fight.

In order to maximize the damage output of your first rotation, you'll have to focus on the Attack Sequence of your DoT arsenal.
The attack sequence of your first rotation will also largely depend on whether Goo awakens, or remains asleep, upon entering its room.

[Note: Golden Bees are not immune to Toxic Gas like Mirror Images are; use at your own discretion.]

1st Rotation:
→ If awoken upon entry, open with Bleeding, then throw T-Gas to the furthest corner from the door, then inflict Poisoned, then inflict Burning, then zap Flock to the same corner you threw the T-Gas, then zap Amok on Goo (if Bleeding/Poisoned/Burning missed the first time, try again after inflicting Amok), then summon Mirror Images, then throw Honeypot at Goo, then attack Goo when there's an opening.
→ If asleep upon entry, open with throwing T-Gas potion at Goo (provided if Goo's far away from the door; if not, follow the attack sequence for Awake Goo), then Bleeding, then Poisoned, then Burning, then zap Flock at the furthest corner, then zap Amok at Goo (if Bleeding/Poisoned/Burning missed the first time, try again after inflicting Amok), then summon Mirror Images, then throw Honeypot at Goo, then attack Goo when there's an opening.

Don't forget to pick up Lloyd's Beacon, if Goo dropped it, and make sure you find & raid/loot the Rat King's room before descending to D-6/Stage 2/Prison stage. This would also be the perfect time to identify any unidentified scrolls, if you haven't already done so at D-4.
If you're trying to save gold, feel free to purchase the unidentified scrolls at the D-6 Shop before identifying them here at D-5.
The downside to that, though, is that you may end up wasting more gold by wasting a scroll like Magic Mapping at D-5.
So the choice is yours, on whether you want to save money by buying unidentified scrolls, but risking a "Russian Roulette" (e.g. Challenge scroll) by identifying them at D-6, or taking a small hit in gold, but playing it safe, so that you don't waste any needed scrolls (e.g. Magic Mapping scroll).

[Note: Allied Summon NPC's are not immune to Paralytic Gas; use at your own discretion.]

Along with Invisibility, this is likely the simplest, most common, & most straightforward method in the bunch. (And hopefully, your Paralyzed source is a P-Gas potion.)

Enter the room, throw/fire your source of Paralyzed, then inflict your DoT arsenal (Poisoned, then Burning, then Bleeding), then attack with your main ranged weapon. Reapply the debuffs when they end; and summon your Allied NPC's if the P-Gas ends before Goo's defeated.

Repeat the rotation until Goo's defeated.

Don't forget to pick up Lloyd's Beacon, if Goo dropped it, and make sure you find & raid/loot the Rat King's room before descending to D-6/Stage 2/Prison stage. This would also be the perfect time to identify any unidentified scrolls, if you haven't already done so at D-4.
If you're trying to save gold, feel free to purchase the unidentified scrolls at the D-6 Shop before identifying them here at D-5.
The downside to that, though, is that you may end up wasting more gold by wasting a scroll like Magic Mapping at D-5.
So the choice is yours, on whether you want to save money by buying unidentified scrolls, but risking a "Russian Roulette" (e.g. Challenge scroll) by identifying them at D-6, or taking a small hit in gold, but playing it safe, so that you don't waste any needed scrolls (e.g. Magic Mapping scroll).

Unlike Paralyzed, this is likely the rarest, least-considered method in the bunch; & is 2nd to Crippled/Slowed in requiring the most movement.
Like with Crippled/Slowed & Rooted, you'll need many Recharging scrolls and/or an upgraded Ring of Power in order to keep blinking through the entire fight.
You'll also need a strip/patch of water to blink back & forth on, as this method necessitates being hit by Goo to proc Charmed from the Affection glyph.
This method also requires careful attention to one's attack sequence, in order to maintain distance for more turns, increasing your damage output.

1st Rotation:
→ If asleep upon entry, open with Bleeding, then feel free to follow-up with Poisoned, then Burning, then Golden Bees & Mirror Images, before closing the distance, to allow Goo to hit you, in order to proc Charmed.
→ If awoken upon entry, skip Bleeding & inflict the rest of your DoT arsenal in the same order, then allow Goo to proc Charmed.

[Note: Be sure that you're standing on a water tile whenever Goo hits you, to proc Charmed, in order to immediately wash off Caustic Ooze before proceeding to the rest of the rotation & fight.]

Don't forget to pick up Lloyd's Beacon, if Goo dropped it, and make sure you find & raid/loot the Rat King's room before descending to D-6/Stage 2/Prison stage. This would also be the perfect time to identify any unidentified scrolls, if you haven't already done so at D-4.
If you're trying to save gold, feel free to purchase the unidentified scrolls at the D-6 Shop before identifying them here at D-5.
The downside to that, though, is that you may end up wasting more gold by wasting a scroll like Magic Mapping at D-5.
So the choice is yours, on whether you want to save money by buying unidentified scrolls, but risking a "Russian Roulette" (e.g. Challenge scroll) by identifying them at D-6, or taking a small hit in gold, but playing it safe, so that you don't waste any needed scrolls (e.g. Magic Mapping scroll).

This Crowd Control tactic can also be combined with other tactics (namely Crippled/Slowed & Rooted), in order to get more turns & distance from Goo.

[Note:
This method will require mindfulness of the water tiles within a 10-cell 'radius' of your Hero/ine.
Especially depending on where you decide to initiate the fight (in Goo's Room, or in the hallway).]

This is one of the four main ranged methods; and has a few layers of depth to it - the most out of the bunch (complex, but easy).

Goo's Room:
→ If Goo's asleep upon entry, initiate the fight by throwing a Tomahawk at Goo, to inflict Bleeding, then immediately follow-up by throwing a T-Gas potion at the opposite end of the room; then immediately follow-up with inflicting Poisoned, then Burning, then attack it with your main ranged weapon, then summon your Allied NPC's right before it reaches melee range.
→ If Goo's awoken upon entry, initiate the fight by throwing a T-Gas potion at the opposite end of the room, then follow-up with inflicting Poisoned on Goo, then Burning, then summon your Allied NPC's right before it reaches melee range. Inflict Bleeding by either stepping out of the room, or on the 10th turn of Terror, right before it ends.

Once you've unleashed your DoT arsenal on the first rotation, read a Terror scroll, or start attacking with your Eldritch-enchanted Boomerang.
Once you've procced Terror on Goo, stop attacking & let Goo run away from you & into the toxic gas, while the rest of the debuffs you inflicted + Allied Summons deal damage to it. Once Terror wears off, re-inflict your DoT arsenal, followed-up with attacking with your main ranged weapon and/or inflicting Terror again.

D-5 Hallway:
[Note: This can only be done with a (mostly) dry hallway. Also, the hallway should already be cleared of traps before initiating the fight. And hopefully, the hallway is at least 10 cells long, so Goo stays in the hallway & doesn't retreat to its room because of Terror.]
If choosing to fight in the hallway, you can either wake Goo up in-person, or via Scroll of Challenge.

→ If asleep upon entry, wake it up with a Tomahawk to the face..err..to its gelatinous body, inflicting Bleeding, then immediately follow-up with Poisoned, then Burning, then your Allied summons, to buy some turns.
→ If awoken upon entry, immediately inflict Poisoned, follow-up with summoning Mirror Images & Golden Bees.
Then immediately back out of the doorway & head to the other end of the hallway (hopefully on a single water tile; up to you to use an Earthroot seed).

Be mindful of the turns it'll take for Goo to clear your summons, before it exits its room; and be sure to throw a T-Gas potion by the door (in the hallway), before it exits the room to follow you into the hallway - this will provide additional DoT as it follows in pursuit of you.
Plant DoT seeds on the way to the opposite end of the hallway, where you'll stand.
Then attack Goo with your main ranged weapon as it approaches you (if you're using an Eldritch-enchanted Boomerang, you might want to wait to use it until it's a lot closer, or until it has stepped on your plant traps).
Once it's close enough, inflict Terror & let your inflicted debuffs deal damage while it runs away; replant any DoT seeds while it's moving away from you.
Then attack it with your main ranged weapon as it re-approaches you, following up with your DoT arsenal ( Bleeding, Poisoned, Burning), then following up with Terror.

Kiting - Challenge Scroll Ranged:
Once the hallway is cleared of traps & you've planted your own, position yourself at the end of the hallway, opposite from Goo's room.
(Depending on your performance, you may, or may not, want to stand on an Earthroot in water.)

Read the Challenge scroll to beckon Goo to you (This may require tapping the Wait button a few times).
As soon as Goo enters the hallway, throw a Tomahawk at it to inflict Bleeding, then immediately throw a T-Gas potion midway between you & Goo.
Immediately proceed to attack it with your main ranged weapon, as it makes its approach to you (if it's an Eldritch-enchanted Boomerang, wait 'til it's closer).
Not only will Goo be subjected to your ranged attacks & forced to trigger your traps, but it'll be forced to walk through the toxic gas as well.
By the time Goo reaches you, it'll be significantly damaged, expediting the fight.
Before it reaches melee distance of you, inflict the Terror debuff & make Goo walk through the toxic gas again.
And as it walks away, reset your DoT plant traps for Goo to walk on again, as the Terror debuff ends & it returns to you.

This method will be most effective (in recalling Goo) with a decent supply of Challenge & Terror scrolls, or an Eldritch-enchanted Boomerang, as you'll have Goo walking back & forth in the toxic gas, with DoT debuffs, essentially making Goo end itself.

Repeat the rotation until Goo's defeated.

Don't forget to pick up Lloyd's Beacon, if Goo dropped it, and make sure you find & raid/loot the Rat King's room before descending to D-6/Stage 2/Prison stage. This would also be the perfect time to identify any unidentified scrolls, if you haven't already done so at D-4.
If you're trying to save gold, feel free to purchase the unidentified scrolls at the D-6 Shop before identifying them here at D-5.
The downside to that, though, is that you may end up wasting more gold by wasting a scroll like Magic Mapping at D-5.
So the choice is yours, on whether you want to save money by buying unidentified scrolls, but risking a "Russian Roulette" (e.g. Challenge scroll) by identifying them at D-6, or taking a small hit in gold, but playing it safe, so that you don't waste any needed scrolls (e.g. Magic Mapping scroll).

Like Paralyzed, this is also a very simple & straightforward (yet uncommon, as it's a relatively new) method.

1st Rotation:
→ If Goo's asleep upon entry, initiate the fight by inflicting Bleeding with a Tomahawk, then immediately follow-up with throwing a Dreamweed seed in Goo's path towards you. Then, throw your Honeypot(s) at Goo; then immediately inflict Poisoned, and then Burning.
→ If Goo's awoken upon entry, immediately throw a Dreamweed seed in its path to you, then follow-up with the DoT debuffs - Poisoned, then Burning, then Bleeding.

Then attack Goo with your main ranged weapon until the DoT debuffs, or the Confusion gas/ Vertigo, ends.
Once the Vertigo debuff ends, or the Confusion gas dissipates, & Goo hasn't been defeated yet, immediately throw another Dreamweed seed in its path, so it doesn't head for you. Only summon Mirror Images between rotations.

Don't forget to pick up Lloyd's Beacon, if Goo dropped it, and make sure you find & raid/loot the Rat King's room before descending to D-6/Stage 2/Prison stage. This would also be the perfect time to identify any unidentified scrolls, if you haven't already done so at D-4.
If you're trying to save gold, feel free to purchase the unidentified scrolls at the D-6 Shop before identifying them here at D-5.
The downside to that, though, is that you may end up wasting more gold by wasting a scroll like Magic Mapping at D-5.
So the choice is yours, on whether you want to save money by buying unidentified scrolls, but risking a "Russian Roulette" (e.g. Challenge scroll) by identifying them at D-6, or taking a small hit in gold, but playing it safe, so that you don't waste any needed scrolls (e.g. Magic Mapping scroll).

This Crowd Control tactic can also be combined with other tactics (namely Crippled/Slowed & Invisible), in order to get more turns to attack Goo & remain safe.

[NOTE:
This only works with Missile Weapons, like the Huntress' Boomerang. Firing wands will prematurely end your Hero/ine's invisibility; only use wands when the Invisible buff is down.]

Along with Paralyzed, this is the simplest, most common, & most straightforward method in the bunch.

Enter Goo's room & initiate the fight by: 1inflicting Poisoned (if with the wand), 2then Burning (wand) {if not from wands, initiate with your Honeypot(s) & Mirror Images first, and inflict Poisoned & Burning after turning invisible}, 3then turn invisible, 4immediately follow-up with Bleeding, 5then attack with your Boomerang until Invisibility ends.6Drink another Invisibility potion if it ends before Goo is defeated.
If your DoT sources are from wands, fire them when invisibility is down; otherwise, feel free to inflict them while invisible.

Repeat the rotation until Goo's defeated.

Don't forget to pick up Lloyd's Beacon, if Goo dropped it, and make sure you find & raid/loot the Rat King's room before descending to D-6/Stage 2/Prison stage. This would also be the perfect time to identify any unidentified scrolls, if you haven't already done so at D-4.
If you're trying to save gold, feel free to purchase the unidentified scrolls at the D-6 Shop before identifying them here at D-5.
The downside to that, though, is that you may end up wasting more gold by wasting a scroll like Magic Mapping at D-5.
So the choice is yours, on whether you want to save money by buying unidentified scrolls, but risking a "Russian Roulette" (e.g. Challenge scroll) by identifying them at D-6, or taking a small hit in gold, but playing it safe, so that you don't waste any needed scrolls (e.g. Magic Mapping scroll).

TL;DR

1.) When available (acquire the items that can) inflict Crowd Control debuffs to immobilize/pacify Goo.

2.) Do your best to acquire the items that will apply the necessary protective buffs to your Hero/ine.

5.) ** Repeat the rotation/Reapply the debuffs, if they end before you defeat Goo.

Step 1 can be skipped, if lacking any items that inflict immobilizing/pacifying debuffs.
Step 3 can also be skipped, if lacking any items that inflict damage-over-time. However, the fight will last significantly longer.
Depending on the strategy, Step 2 can also be skipped, but it'll also make the fight last much longer & it'll likely hurt a lot more, too.

Ultimatecub wrote:Then what do you use scrolls of upgrade on, plate armor?

Yes. 6 on Plate (if base level), or until Plate is +6 (if Plate is already upgraded when obtained).

If you've found a Plate that's already +1, +2, or better yet, +3, then you've found your end-game armor.
Upgrade it to +6 (not all at once, but incrementally & evenly with your main item, as you descend deeper & get more scrolls), and use your remaining Upgrade scrolls on either your main melee weapon/Battle wand/boomerang/ring(s).

Ultimatecub wrote:The time I beat Goo I had both an Earthroot and Sorrowmoss, but that fight was in the corridor and I didn't have anywhere to get away from Goo's pumped up attack.

I had a seed of Earthroot once and was standing on it, then Goo started pumping up and I ran away, then after I stepped off it the plant vanished.

In the corridor I had to:1. step off the Earthroot plant to escape from the pumped up attack (then the plant vanished)2. when Goo started pumping up I ran away straight away but then Goo used the next turn to run after me...

.. It's clearly stated on the Seed of Earthroot page that you're not supposed to step off of the Earthroot plant once you step on it, until you've defeated Goo. Stepping off of it prematurely will remove your Herbal Armor buff, leaving your Hero unprotected (& you won't get the buff back unless you replant another seed & step on it).

You only run away if you don't have an Earthroot seed to protect you in the boss fight in the first place.

Next time you fight Goo, once you step on the Earthroot plant, stay in place until you've defeated Goo (& make sure you plant the Earthroot seed on a water tile, so the water can wash off Caustic Ooze).

I just started a new game just before I read this, and was trying the weapon approach and have what I think is a +3 or +4 sword (not short sword, regular sword.) Just giving it a try not upgrading the armor just to see what happens.

I have a Seed or Earthroot, 2 Sorrowmoss, 1 Dreamweed, 1 Sungrass, just turned invisible from a frozen carpaccio, and have just entered Goo's room and it is standing on water and practically the whole room is flooded with water unfortunately. Just went to this page to read the guide to see what to do now.

Ultimatecub wrote:...practically the whole room is flooded with water unfortunately.

Simple. If the whole room is flooded, you need to lure Goo out of the room, and then you need to make a U-turn, so that you return to his room, with you standing on water, and Goo standing in the doorway, so he's not standing on water.
(Be sure that before you step into the room, from the doorway, that you throw the Earthroot seed to an adjacent water tile first, so you can step on it when you step into the room; sequence is key.)

Obviously not, if you're still posting the same explanation on multiple different threads, rather than in here.

Please don't duplicate your game explanations on multiple threads, especially if the topic of the thread you're posting in isn't directly related to what you're posting about. You're only derailing each thread's topic.

For further descriptions of your attempts at defeating Goo, please post them in this thread, and not the other threads you've been posting them in.

I just resumed the game I was playing yesterday (loads of seeds, wand of firebolt, eldritch sword +3, flooded room) and planted a seed of earthroot outside the door, woke up Goo and planted a Seed of Sorrowmoss in the doorway. Was 2 hits away from killing Goo, then Goo pumped up and killed me. But I didn't step off the Earthroot at all...

I put a Seed of Sorrowmoss in the doorway and a Seed of Earthroot on a water tile behind it, woke Goo up and made it step on the SoSRM. I didn't move off the SoE at all in the whole fight and was going to beat Goo in the next 2 or 3 hits then Goo killed me when my health wasn't actually that low.

I made Goo step on a Sorrowmoss plant in the doorway and was standing on a seed of Earthroot on water. I didn't step off the Earthroot plant at all. I had a +3 Eldritch enchanted regular sword (13 damage - was trying the weapon-upgrade approach) and was 2 hits away from killing Goo when it killed me with a pumped up attack. I was watching the buffs, and I had the herbal armor buff the whole time.

Yes, but as SS99 mentioned, sometimes Goo's attacks will penetrate the Herbal Armor buff.
That's when drinking a Potion of Healing is needed.
Did you not have any Potions of Healing to drink during the boss fight (or a Full Dew Vial for that matter)?
Because you still need them, especially if you're still at novice-level of fighting Goo.

Also, it'll be easier for Goo to inflict more damage on you if your armor is low, even with the Herbal Armor buff.
That's why I provided the specifics of how much armor absorption you need, to face him, because focusing on only upgrading your main weapon is too risky, especially for novice players (it's an advice that's only good for veterans, who know how to manage other factors/variables besides weapon level or damage absorption).

Review my guide (more carefully this time around), then contrast what it says with what you did & pinpoint where you went wrong in your fight, so you can make the necessary adjustments.

I was playing as a Warrior and watched CJTC's Huntress video. I think he just threw a golden bee honeypot at Goo and then finished Goo off afterwards. I tried that today. I threw the honeypot at Goo and the golden bee got rid of about half Goo's health. Then it said "You heard something died in the distance" so my bee died (how tragic) and I went in to finish off Goo. I had a Shocking short sword and +2 Scale Armor but not a seed of Earthroot. I put a seed of Firebloom and Sorrowmoss in its way and it stepped on them. I did have a healing potion and I drank that when I was down to 7HP but every single turn Goo started pumping up and even though I ran away, Goo still killed me.

Sorry if I omitted something in the guide, I wasn't at home when I was fighting Goo and didn't have an internet connection. My scale armor absorbed 12 or 13 damage and my short sword was 6 or 7 damage, so as close as I could get to 8.

I'm probably being COMPLETELY clueless right now because I don't know how you're supposed to identify potions, because I identified them all at depth 4 near the stairs down, but I wasted a paralytic gas potion and an invisibility testing them out (fortunately I still had 2 more invisibility, but still.)

The thing is, in the Rankings it says I had cloth armor. I'm 100% sure my scale armor didn't break (I checked when I got down to depth 5, it was still nowhere near degradation and I didn't unequip it.)

Ultimatecub wrote:The thing is, in the Rankings it says I had cloth armor.I'm 100% sure my scale armor didn't break (I checked when I got down to depth 5, it was still nowhere near degradation and I didn't unequip it.)

That's strange. That definitely seems like a bug that you should report to Watabou, so he can investigate the issue.

I'm probably being COMPLETELY clueless right now because I don't know how you're supposed to identify potions, because I identified them all at depth 4 near the stairs down, but I wasted a paralytic gas potion and an invisibility testing them out (fortunately I still had 2 more invisibility, but still.)

(Yeah, I need to amend the Sewer Stage Guide I wrote, so please bear with me on that, but..)
You'll want to identify your potions as soon as you start the game.
(Healing & Strength potions are relatively easy to identify if you consistently see a particular color potion at almost each depth - See the Tips section of each potion's page.)

If you checked the link to the Dungeon Guide that I provided for you (which this wiki's Main Page also has a direct link to), there's a link there that leads to tips on identifying items. That should help.
And for specifically identifying potions, visit the Tips section of the Potions page.

One more thing; make sure you scour the wiki for the answer(s) you're looking for, before you ask anything; because chances are, it's already answered for you somewhere on this wiki.
(Plenty of the pages on this wiki have a Tips section you can read.)

Thanks and I don't want to digress so is there a better place to put this post? That one about Potions of Healing mentions farming flies and the time I beat Goo I found some in the Sewers (really unlikely) and identified the PoH but if you don't have flies, seems harder.

Just got to D-5 with quite a good run. 3 potions of liquid flame, 1 Sorrowmoss seed, 1 Earthroot seed, 1 potion of invisibility, 3 bombs, a +4 Ring of Haste and a Shocking short sword. (My bad luck.)

Just asking, is the reason that the Shocking enchantment is not recommended because for Goo to take the most damage from it it'll have to be standing in water and you wouldn't want that because it heals? I couldn't find it on the Enchantment page.

(Thinking of drinking Invisibility then chucking bombs and the liquid flame potions and using the seeds because I don't seem to have the equipment for any of the above described methods by a small margin :( Will probably just go for the TL:DR.)

Ultimatecub wrote:...is the reason that the Shocking enchantment is not recommended because, for Goo to take the most damage from it, it'll have to be standing in water; and you wouldn't want that because it heals?

Yes, correct.

I couldn't find it on the Enchantment page.

Couldn't find what on the Enchantment page?

That Shocking deals double damage when the enemy is on water, or that Goo heals when on water?

If the former, then it is on the Enchantment page, in the chart. If the latter, then of course it isn't; it's on Goo's page.

______________________________________

I'm just surprised at your "luck", in how often you keep getting the Shocking enchantment on your Short Sword.

If you can find yourself (not upgrade) a +2 Quarterstaff & a +2 Mail Armor, along with an Earthroot seed, a couple of Healing potions, & DoT items, you should be set to go.

I couldn't find the exact reason why Shocking wasn't recommended on the Enchantment page. The reason I mentioned was just a hypothesis I came up with. By the luck thing I meant that I got an enchantment that wasn't recommended for the fight.

Yeahh, noo.. That info wouldn't be on the Enchantment page. It'd be on Goo's page because it specifically concerns Goo.

The reason I mentioned was just a hypothesis I came up with.

And you hypothesized correctly. =)

By the luck thing, I meant that I got an enchantment that wasn't recommended for the fight.

Yeah, I picked up on that.

The enchantments you'd want (for Warrior) against Goo are pretty much any of them except Eldritch, Shocking, & Unstable. And you'll only want to avoid Blazing if your armor has the Bounce glyph & you're using the door's Surprise Attack mechanism in the fight.

Thanks so much! I beat Goo again and seems everything worked exactly as planned. Didn't even take a single hit from Goo, the bombs and the liquid flame potions did all the work. Probably didn't even need to waste the Seed of Earthroot. Thanks! Probably not going to last that long in Stage 2 because I still only have a short sword and cloth armor with the shop selling an overpriced leather armor for 400 gold.

Thanks Shadow Automaton again! I beat Goo today with a Short Sword and +3 Scale Armor from the Sad Ghost. Am now on D-6 where the armor is about to break and I have no armor repairing items. Am going to make another topic about degradation.

Can someone please explain to me what "Heroes remains" are?
I'm relatively new to the game (have been playing it for about a week now) but I never saw that feature in the game. Or at least I didn't recognise it